1. Field of the Invention
The invention relates to a shift control system and shift control method that control a shifting mechanism provided in a drive-train of a vehicle. More particularly, the invention relates to a shift control system and shift control method that cause the shifting mechanism to shift multiple gears in response to an input operation and to selectively make a skip shift.
2. Description of Related Art
In an automatic transmission mounted on a vehicle, there is known a shift control system or a shift control method that selectively executes automatic shift control and manual shift control. In the automatic shift control, rotational power from a driving source is automatically shifted in speed among multiple gears on the basis of an accelerator operation amount and a vehicle speed. In the manual shift control, rotational power from the driving force is shifted in speed among multiple gears on the basis of a manual operation input by a driver. In addition, by employing a by-wire technology, a shift control system or a shift control method that is able to make a sequential upshift or downshift in one gear (sequential shift) not only by operating an existing shift lever but also by operating a paddle or a switch provided on a steering wheel has been widely used.
There is a shift control system of this type, for example, which is able to make a skip shift. In the skip shift, when a sequential shift operating lever is quickly operated multiple times successively, a transmission path of a gear finally selected by the multiple operations is directly formed without forming a transmission path of a gear selected on the way (for example, see Japanese Patent Application Publication No. 05-235794 (JP 05-235794 A) and U.S. Pat. No. 5,415,604).
Furthermore, there is known a shift control system that, when it is predicted to enter a driven state where an internal combustion engine is driven by a drive wheel side to accelerate if a skip shift is made to a gear finally selected through successive multiple downshift operations input to a downshift switch, prohibits a downshift to the finally selected gear and a gear having a higher gear ratio than the finally selected gear (for example, see Japanese Patent Application Publication No. 2010-266045 (JP 2010-266045 A)).
However, in these shift control systems and shift control methods, there are many number of times of sequential shifts in an automatic shift mode, so a response to a driver's acceleration request, or the like, is not sufficient. In addition, when a skip shift to a gear that causes a driven state is requested through an input shift operation, it is not possible to respond as requested. Furthermore, even when a skip shift to a gear that does not cause a driven state is requested through an input shift operation, an acceleration or deceleration of a vehicle through the skip shift may differ from a degree of acceleration or deceleration intended by a driver, so there is a possibility that it is not possible to sufficiently improve drivability.
That is, when the number of gears of an automatic transmission increases, the number of intervening gears increases when a sequential shift to a required gear is made in the automatic shift mode. Therefore, a plurality of hydraulic frictional engagement elements in the automatic transmission repeatedly turn on or off (engage or disengage) such that intervening gears are sequentially formed. Thus, a response to a driver's acceleration request, or the like, may not be sufficiently obtained.
In addition, when the number of gears increases, a deceleration expected by the driver is hard to match with a driver's request operation depending on a set gear step (difference (change width) in gear ratio between adjacent gears) between multiple gears. Then, when a deviation between a deceleration expected by the driver and a driver's request operation increases through successive multiple shift operations, an acceleration or deceleration of the vehicle through a skip shift may tend to differ from a degree of acceleration or deceleration intended by the driver.
In addition, such a situation that an acceleration or deceleration of the vehicle before and after a skip shift differs from a degree intended by the driver may occur even when a skip shift is made through a shift command based on an acceleration request operation in the automatic shift mode.